1. History of the Earth Early conditions (~4.6 billion years ago)
High temperatures
Volcanoes, Earthquakes
Early atmosphere
High levels of gases not compatible with life
No OXYGEN!

2. Earliest evidence of life
~3.5 billion years ago
Ancient prokaryotes, similar to modern bacteria
Found in the ocean
How did they get there in this inhospitable environment?
Two different theories: abiogenesis vs. biogenesis

3. ABIOGENESIS Simple molecules randomly combined and separated
Larger, more complex molecules formed
When these were able to reproduce, life was formed
Proved in experiment by Miller and Urey (1953)
Produced organic compounds similar to those of early Earth

4. Another theory…BIOGENESIS
The idea that life comes from pre-existing life
Redi (1668) observed that maggots (larval fly form) only appeared on meat that was exposed to flies

5. Biogenesis…continued
Further confirmed by Spallanzani and Pasteur, who also showed that life does not arise from nonlife
You simulated this lab back in Week 1!

6. So what were the first organisms like?
First organisms were
prokaryotic (extremely simple!)
heterotrophs
Rely on consuming compounds to obtain energy
anaerobic, meaning they did not need oxygen to survive (a good thing because there was no oxygen in the atmosphere!)

7. Oxygen (02)
Over the next billion years, atmospheric oxygen increased from 1-21%
O2 important because reactions using oxygen allow organisms to use chemical energy more efficiently
Development of autotrophs appeared (3-3.5 bil yrs)
Created organic chemical energy from inorganic compounds
O2 allowed the development of mitochondria, which use O2 to process energy. These cells would be eukaryotes with membrane-bound organelles

8. How did bacteria evolve into the living organisms we see today?
Over millions of years natural selection resulted in the variety of life we see today
Organisms with characteristics that favor survival pass those characteristics to offspring
Originally proposed by Charles Darwin
Changes came about in spurts due to environmental changes

9. Evolution
Existing organisms adapt and become new species as they fill niches left by extinct species through evolution
The theory that explains how organisms change over time

10. Charles Darwin
Went around the world in a ship called the Beagle and collected observations of different organisms
Most important work was with the finches of the Galapagos Island
Darwin observed that
all of the finches were
similar except for their
beaks.
Muskopf, Shannan. Online Images. The Biology Corner. 13 May 2007.

11. Darwin’s Observations
Organisms adapt to their environment
Finches had adapted beaks to eat the available food in their environments
Some species that do not adapt do not survive
“Survival of the Fittest”
Fitness refers to the physical traits and behaviors that help an organism to survive and reproduce in its environment
Called “Natural Selection” because the environment or nature selects how well the traits of an organism will help it survive; organisms without those traits are less “fit” and may not survive

12. The “spunk” animals in the figure have different traits.
The environment or the food selects for tall spunks while the short spunks are at a disadvantage because they can’t reach the food.
The tall spunks are better suited to their environment and will survive to reproduce more offspring.
The less “fit” or short spunks will not survive, so their DNA will not be passed on. Over time, the population will be all tall spunks.
Online Images. Welcome Trust. 13 May 2007.

13. Darwin’s key ideas: VARIATION: variety in traits exist
STRUGGLE FOR EXISTENCE: members of a species compete for resources (food and living space); Competition leads to the death of those less fit
SURVIVAL OF THE FIT: individuals best suited to their environment survive & reproduce

14. Evidence for Evolution
1. Fossils: provide indirect evidence that modern species evolved from ancient organisms that are now extinct

15. How do we know how old a fossil is?
Absolute or radioactive dating uses isotopes to provide a general age of how old a rock might be
Isotopes break down over time
Remaining amounts can be analyzed to determine a rock’s age
Relative dating uses rock layers to show which fossils are more recent than others

16. 2. Homologous Structures: structures with similar bone arrangements but different functions; the similarity is evidence that they came from a common ancestor
Ex: the forearms of a human, cat, whale, and bat have similar bone arrangements but are used for different things
Muskopf, Shannan. Online Images. The Biology Corner. 13 May 2007.

17. 3. Analogous Structures: structures that do not have a common ancestor but develop similar structures because they are in similar environments
Example of Analogous Structures: the wings of pterosaurs, bats, and birds have similar structures but did not come from a common ancestor
Online Images. Wikipedia. 13 May 2007.

18. Vestigial Structures: a body structure that has diminished in size or usefulness
Ex: appendix or the pelvic bone in a whale (these
structures have no function)
Muskopf, Shannan. Online Images. The Biology Corner. 13 May 2007.

19. 5. Embryology: the study of organisms in early stages of development; related organisms will have similar embryos
In the early stages of development (top pictures), the fish, salamander, hog, rabbit, and human look similar, providing evidence that they came from a common ancestor.
Online Images. Wikipedia. 13 May 2007.

20. 6. Biochemistry and DNA: similar DNA or amino acid sequences between two organisms is evidence that the two organisms came from a common ancestor

21. Okay, so there is evidence evolution has occurred
Okay, so there is evidence evolution has occurred. But HOW did it happen?
Populations Evolve, Not Individuals
An individual organism cannot evolve but is part of a population that will evolve over time
Each individual has genes that characterize the traits of their species
Evolution occurs as a population’s genes and their frequencies change over time

22. Originally, there was variation in neck length
Originally, there was variation in neck length. Over a long time, the population of giraffes evolved to have long necks because long necks are selected for by the environment. An individual giraffe can not stretch his neck and evolve, only a population of giraffes can evolve to have longer necks over many, many generations.
Muskopf, Shannan. Online Images. The Biology Corner. 13 May 2007.

23. How do populations genes change?
Gene pool: all of the genes in a population
For evolution to occur, the percentage of a gene in the gene pool must change
A population in which the frequency of genes remains the same over generations is in genetic equilibrium and does not evolve

24. Changes in Genetic Equilibrium Causes Evolution
A population in genetic equilibrium is not evolving
One cause of evolution is a mutation (a change in the DNA)
A mutation provide the opportunity for an organism to have a trait that increases its chances of survival (ex: stronger beak to eat seeds). Trait is passed to offspring through its DNA.
Organisms without the mutation may not be able to get food, for example, and will die, not passing along their DNA
“Survival of the Fittest”!

25. Natural Selection is the biggest cause of Evolution!
Darwin observed that
all of the finches were
similar except for their
beaks. The environment (available food) will select the type of beak that will enable a finch to survive and reproduce. Over time, the finches that do not have the “fit” beak will not survive and reproduce.
Muskopf, Shannan. Online Images. The Biology Corner. 13 May 2007.

26. Speciation: formation of new species
Cause of speciation:
Behavioral Isolation - occurs when two species have different courtship behaviors (males have courtship songs or dances that will only be recognized by females of the same species)
Geographic Isolation – physical barrier (river, mountain) prevents contact between individuals and leads to speciation

27. Pesticide or antibiotic resistance: bacteria become resistant to pesticides (sprayed on crops) and antibiotics and survive
Originally, there are a variety of bacteria. The pesticide or antibiotic kills all of them but the dark red bacteria. These resistant bacteria survive and reproduce and eventually the population evolves and is made up of resistant dark red bacteria.
Online Images. Wikipedia. 13 May 2007.